1. Field of the Invention
This invention relates to a device for measuring optical reflectance values of a test object and/or measured values derived therefrom and more particularly to a spectrophotometer.
2. State of the Art
Measuring devices, such as spectrophotometers of the type of the present invention, have been described in U.S. Letters Pat. Nos. 4,968,140, 4,961,646 and 4,929,084 (corresponding to European Patent Publications EP-B-0 328 483, EP-B-0 331 629 and EP-B-0 327 499). These computer-controlled measuring devices are embodied as hand-held devices and have a movable measuring head which is extended out of a housing for the measurement process and is subsequently retracted into the housing.
As with many measuring instruments, measuring devices of the type in accordance with exemplary embodiments of the present invention need to be regularly calibrated or checked with respect to their spectral calibration if the dependability of the measured results is to be assured. This is achieved by measuring special calibration test objects (calibration standards) matched to the respective measuring device, which are provided as separate components of the measuring device. These measured values are evaluated by the computer in connection with corresponding stored reference values, in order to either obtain a statement regarding the properties of the measuring device to be checked, or to perform calibration automatically, provided the measuring device is equipped with such functions.
These calibrating and checking processes require special care and regularity. These processes must be performed within prescribed time intervals, and the positioning of the measuring device, or its measuring head, relative to the calibration test object must be correct, so as not to affect the measured results negatively.